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Velislav N Batchvarov

Publications and source records attributed to Velislav N Batchvarov.

8 recordsLinked to original sources
PubMed2006

Precision of QT interval measurement by advanced electrocardiographic equipment.

The costs of clinical investigations of drug-induced QT interval prolongation are mainly related to manual processing of electrocardiographic (ECG) recordings. Potentially, however, these costs can be decreased by automatic ECG measurement. To investigate the improvements in measurement accuracy of the modern ECG equipment, this study investigated QT interval measurement by the "old" and "new" versions of the 12SL ECG algorithm by GE Healthcare (Milwaukee, WI, USA) and compared the results to carefully validated and reconciled manual measurements. The investigation used two sets (A and B) of ECG recordings that originated from large clinical studies. Sets A and B consisted of 15,194, and 29,866 10-second ECG recordings, respectively. All the recordings were obtained with GE Healthcare recorders and were available in digital format compatible with ECG processing software by GE Healthcare. The two sets of recordings differed significantly in ECG quality with set B being substantially more noise polluted. Compared to careful manual QT interval readings in recording set A, the errors of the automatic QT interval measurement were (mean +/- SD) +3.95 +/- 5.50 ms, and +0.51 +/- 12.41 ms for the "new" and "old" 12SL algorithm, respectively. In recording set B, these numbers were +2.41 +/- 9.47 ms, and -0.17 +/- 14.89 ms, respectively (both differences were highly statistically significant, P < 0.000001). In recording set A, 95.9% and 76.6% of ECGs were measured automatically within 10 ms of the manual measurement by the "new" and "old" versions of the 12SL algorithm, In recording set B, these numbers were 83.9% and 59.5%. The errors made by the "new" and "old" version of 12SL algorithm were practically independent each of the other (correlation coefficients of 0.031 and 0.281 in recording sets A and B, respectively). The study shows that (a) compared to the "old" version of the 12SL algorithm, the QT interval measurement by the "new" version implemented in the most recent ECG equipment by GE Healthcare is significantly better, and (b) the precision of automatic measurement by the 12SL algorithm is substantially dependent on the quality of processed ECG recordings. The improved accuracy of the "new" 12SL algorithm makes it feasible to use modern ECG equipment without any manual intervention in selected parts of drug-development program.

Algorithms↗
PubMed2004

Prognostic value of heterogeneity of ventricular repolarization in survivors of acute myocardial infarction.

BACKGROUND: The expansion of indications for implantation of cardioverter-defibrillators (ICD) has enhanced the need for risk stratification of patients post myocardial infarction (MI), while the improved treatment of acute MI has decreased mortality and diminished the prognostic power of traditional risk variables. HYPOTHESIS: Increased heterogeneity of ventricular repolarization quantified by TCRT (total cosine R-to-T, angular difference between spatial QRS and T loops, decreased with increase in repolarization heterogeneity) is an independent predictor of mortality in patients post MI. METHODS: Left ventricular ejection fraction (EF), QRS duration on signal-averaged ECG, number of ventricular ectopic beats (VE)/h, heart rate variability (HRV) triangular index, heart rate turbulence slope on 24-h Holter recording, and TCRT were analyzed in 334 survivors of acute MI followed up for 41 +/- 20 months. RESULTS: In multivariate analysis, EF < 35% (relative risk [RR] 2.3, 95% confidence interval [CI] 1.1-4.7, p = 0.023), VE > 10/h (RR 2.2, CI 1.0-4.6, p = 0.044), HRV < 20 U (RR 2.2, CI 1.1-4.5, p = 0.032), and TCRT < -0.896 (RR 4.3, CI 2.2-8.5, p = 0.00001) were independent predictors of cardiac mortality (11%). Independent predictors of arrhythmic mortality (5%) were VE, HRV, and TCRT (RR 5.8, CI 2.1-15.6, p = 0.0004). Cardiac and arrhythmic mortality of patients with both EF <35% and TCRT < -0.896 were >60 and >30%, respectively, compared with 17 and 7% in those with only EF <35% or TCRT < -0.896. CONCLUSION: Decreased TCRT, which reflects increased repolarization heterogeneity, is a strong and independent predictor of cardiac and arrhythmic death in patients post MI.

Action Potentials↗
PubMed2004

Post infarction risk stratification using the 3-D angle between QRS complex and T-wave vectors.

Present experience with prospective identification of patients who might benefit from prophylactic antiarrhythmic intervention is restricted to risk stratification using left ventricular ejection fraction (LVEF). The precision of LVEF-based identification of high risk patients is neither highly sensitive nor highly specific. This study investigated risk stratification of 466 survivors of acute myocardial infarction (86 women, mean age 57.5 years) for whom a 5-year follow-up was available. During the follow-up 67 patients died and 24 of these events were sudden arrhythmic deaths. In addition to LVEF, patients were stratified by mean heart rate, heart rate variability and the slope of heart rate turbulence, all derived from 24-hour Holter recording obtained before hospital discharge, and by the 3D angle between QRS complex and T wave vectors (total cosine R-to-T, TCRT) obtained from digital resting electrocardiogram before hospital discharge. Individual risk characteristics and their combinations were evaluated by calculating the areas under the receiver operator characteristics (ROC). The bootstrap technology was used to investigate these statistically. For the stratification of both all cause mortality and sudden arrhythmic death, TCRT was the strongest risk stratifier (area under ROC of 0.6857 +/- 0.0367, and 0.7275 +/- 0.0544, respectively) that compared very favourably to LVEF (area under the ROC of 0.6610 +/- 0.0362 and 0.6346 +/- 0.0595, for all cause and arrhythmic death prediction, both P < 10(-10) for the comparison with TCRT). TCRT was also stronger in combination with other stratifiers, eg, TCRT + LVEF (area under ROC of 0.7631 +/- 0.0325 and 0.8057 +/- 0.0473, for all cause and arrhythmic death prediction) was stronger than mean heart rate + LVEF (area under ROC of 0.7396 +/- 0.0298 and 0.7673 +/- 0.0445, respectively, both P < 10(-10) for comparison with TCRT + LVEF). Hence the 3D QRS-T angle is a very powerful risk stratifier especially suited for the prediction of sudden arrhythmic death. It should be prospectively investigated in future trials of prophylactic antiarrhythmic interventions.

Adult↗
PubMed2003

Ventricular gradient and nondipolar repolarization components increase at higher heart rate.

Differences in action potential duration reflect differences in ion channel properties. These properties also determine rate dependence of action potential duration, and transmural dispersion was confirmed experimentally to increase with cycle length. While several electrocardiographic indexes characterizing repolarization abnormalities have been proposed, studies of their heart rate dependence are missing. This study therefore investigated rate relationship of two repolarization descriptors, namely, the so-called total cosine of the QRS-T angle (TCRT), proposed to characterize global repolarization heterogeneity, and the so-called relative T wave residuum (TWR), linked to regional repolarization dispersion. During 24-h holter recordings in 60 healthy subjects (27 males), a 12-lead ECG was obtained every 30 s. RR intervals, QT intervals, and TCRT and TWR were calculated in each ECG and averaged over RR interval bins ranging from 550 to 1,150 ms in 10-ms steps. Women had uniformly greater TCRT and TWR values than men did over the entire range of investigated RR intervals. Whereas the TCRT in both sexes showed marked rate dependence with higher values at long RR intervals (550 vs. 1,150 ms: women, 0.46 +/- 0.31 vs. 0.76 +/- 0.18, P = 9 x 10(-7); men, 0.08 +/- 0.45 vs. 0.49 +/- 0.35, P = 9 x 10(-8)), the rate dependence of TWR was more marked in women than in men, showing higher values at shorter RR intervals (550 ms vs. 1,150 ms: women: 0.29 +/- 0.14% vs. 0.08 +/- 0.06%, P = 2 x 10(-8); men: 0.14 +/- 0.12% vs. 0.04 +/- 0.02%, P = 2 x 10(-15)). This suggests that both global and regional repolarization heterogeneity are increased at faster heart rates. Whereas in women at all heart rates the sequence of repolarization more closely replicates the sequence of depolarization, localized repolarization is more heterogeneous than in men especially at fast heart rates.

Adult↗
PubMed2002

QT-RR relationship in healthy subjects exhibits substantial intersubject variability and high intrasubject stability.

Recently, it was demonstrated that the QT-RR relationship pattern varies significantly among healthy individuals. We compared the intra- and interindividual variations of the QT-RR relationship. Twenty-four-hour 12-lead digital electrocardiograms (ECGs; SEER MC, GE Marquette; 10-s ECG recorded every 30 s) were obtained at baseline and after 24 h, 1 wk, and 1 mo in 75 healthy subjects (42 women, 33 men, age 27.9 +/- 9.6 vs. 26.8 +/- 7.5 yr, P = not significant). QT interval was measured automatically in each ECG by six different algorithms, and the mean of the six measurements was analyzed. In each recording of each individual, QT-RR relationship was assessed by 10 different regression models including linear (QT = beta + alpha x RR) and parabolic (QT = beta x RR(alpha)) models. Standard deviations (SDs) of regression parameters alpha and beta of consecutive recordings of each individual were compared with SD of the individual means. Intrasubject stability and interindividual variability were further tested by ANOVA. With all models, intraindividual SDs of the regression parameters were highly significantly smaller than SD of individual means (P < 10(-5)-10(-9)). The intrasubject stability was further confirmed by ANOVA (P < 10(-19)-10(-30)). The QT-RR relationship exhibits substantial intersubject variability as well as a high intrasubject stability. This has practical implications for a precise estimation of the heart rate-corrected QT interval in which optimized subject-specific rate correction formulas should be used.

Adolescent↗
PubMed2002

Sex differences in repolarization homogeneity and its circadian pattern.

The reason for sex differences in arrhythmic risk remains unclear. Heterogeneity of ventricular repolarization is directly linked to arrhythmogenesis; thus we investigated repolarization homogeneity and its circadian pattern in men and women. During 24-h Holter recordings in 60 healthy subjects (27 males), a 12-lead electrocardiogram (ECG) was obtained every 30 s. RR and QT intervals, and, after singular-value decomposition, two characteristics of repolarization homogeneity were calculated in each ECG. Corrected QT (QTc) values were obtained using an individually optimized heart rate (HR) correction formula. All values were averaged over 10-min time bands from 0000 to 2400. There were substantial sex differences in both global repolarization homogeneity (measured by the total cosine of the angle between QRS and T wave vectors) and regional homogeneity of repolarization (quantified independently by the relative T wave residuum). Whereas women throughout the 24 h followed more closely the pattern of inverse sequence between depolarization and repolarization, they also showed much higher localized repolarization heterogeneity than men. In both women and men, repolarization irregularity was greatest during morning hours. A sex difference was also observed for HR and QTc interval; however, the circadian patterns of the repolarization homogeneity descriptors were different from those of HR and QTc intervals.

Adolescent↗
PubMedDate not supplied

The effect of mental stress on the non-dipolar components of the T wave: modulation by hypnosis.

OBJECTIVE: Mental or emotional stress-induced ventricular arrhythmias and sudden cardiac death are thought to be mediated by the autonomic nervous system and ischemia. In the absence of ischemia, increased inhomogeneity of repolarization is thought to be important. We tested the hypotheses that in the absence of ischemia, mental stress may modulate repolarization by changing autonomic balance; and mental relaxation induced by hypnosis may offset the potentially adverse effects of stress on the cardiac electrophysiology. METHODS: Twelve healthy volunteers (6 male, age 18-35, mean 25 years) experienced a series of different emotions intended to induce a wide range of autonomic response (42 test epochs) on two separate occasions, with and without hypnosis, with continuous electrocardiogram recording. Low- (LF) and HF (high-frequency) heart rate variability was measured and ventricular repolarization was assessed using the relative T-wave residua (proportion of nondipolar components of the T wave) calculated for the T-onset - T peak (TWR-peak T), T peak -T end (TWR-end T), and the whole T wave (TWR). RESULTS: Emotionally induced changes in LF and LF/HF ratio correlated with changes in TWR, e.g., (R = 0.51, p < .001; R = 0.59, p < .0001; and R = 0.59, p < .0003, for LF/HF versus TWR, TWR-Peak T, and TWR-end T, respectively. Mental relaxation induced by hypnosis increased LF power (1,205 ms2) versus 624 ms2, p < .003 for hypnotized versus nonhypnotized state), HF power (1,619 ms2 versus 572 ms2), p < .0004), and reduced LF/HF ratio (1.0 versus 1.5, p = .052) and was associated with a marked reduction in the changes in repolarization in response to emotion, e.g., 10.7 x 10(-6) versus 5.0 x10(-6), p < .03 for TWR. CONCLUSIONS: a) Mental stress in the absence of ischemia altered repolarization inhomogeneity via change in the autonomic balance. b) Mental relaxation induced by hypnosis greatly reduced the effect of mental stress on repolarization. c) These findings may have implications for arrhythmogenesis.

Adolescent↗